This invention relates to microcircuit packages, and, more particularly, to a microcircuit encapsulated within a housing and a method for effecting the encapsulation.
There are presently many different types of microcircuit packages, and a variety of methods for assembling the package about the microcircuit. Glass to metal seal packages, glass-ceramic-metal packages, ceramic to metal packages, and plastic packages are among the most prevalent. The latter technology is primarily used for producing two types of packages. The first type is a premolded package with leads that can be sealed by either gluing or soldering a lid on the package. The second type includes a design in which plastic is formed about a microcircuit by casting or transfer molding. There are disadvantages, however, with both types of plastic packaging. A primary drawback with the soldered or glued package is its general non-hermeticity and lack of mechanical strength. Some of the major difficulties associated with the plastic transfer molded package relate to manufacturing and testing problems.
The metal leads in the soldered or glued package are commonly encased within a small glass coating along at least one side of the package. The leads are typically inserted sidewardly into the package and then bent over an edge. Thus, this assembly can be subjected to rather severe mechanical stress.
In the manufacture of plastic transfer molded packages, molding voids frequently result. Also, molding imperfections -- such as flashes -- are commonly incurred. Since, according to this technique, the plastic package is formed about the microcircuit, if the package must be discarded due to voids or imperfections caused by molding operations, then an otherwise adequate microcircuit becomes wasted. The microcircuit is the most expensive component in a packaged assembly, and the abandonment of a package containing a microcircuit which tests satisfactorily is a needless expense that adds to overall production costs.
If, on the other hand, the package defects or deficiencies are not sufficiently serious to warrant rejection, but are correctable, then labor costs must be incurred in rectifying the package so that the assembly will merit customer approval. Thus, these labor costs accrue when the cost of cleaning the package -- such as filling voids or removing flashes -- is less than the cost of rejection of the entire assembly including the microcircuit. Therefore, even minor package defects can lead to increased overall production costs in the form of labor costs.
Hence, package defects, resulting from molding operations, cause an increase in production cost --either capital or labor. This is particularly disadvantageous in the field of microcircuit packaging in that one of the most important features in this field is low cost.
Furthermore, since, according to this method, the plastic package is formed about the microcircuit, the fragile microcircuit components are exposed to molding temperatures and pressures which may have deleterious effects on these components.